There is a continuous development of new generations of mobile communications technologies to cope with increasing requirements of higher data rates, improved efficiency and lower costs. High Speed Downlink Packet Access (HSDPA) and High Speed Uplink Packet Access (HSUPA), together referred to as High Speed Packet Access (HSPA), are mobile communication protocols that were developed to cope with higher data rates than original Wideband Code Division Multiple Access (WCDMA) protocols were capable of. The 3rd Generation Partnership Project (3GPP) is a standards-developing organization that is continuing its work of evolving HSPA and creating new standards that allow for even higher data rates and improved functionality.
In a radio access network implementing HSPA, a user equipment (UE) is wirelessly connected to a radio base station (RBS) commonly referred to as a NodeB (NB). A radio base station is a general term for a radio network node capable of transmitting radio signals to a user equipment (UE) and/or receive signals transmitted by a user equipment (UE).
In multi-cell HSPA (MC-HSPA) systems a NodeB, alternatively referred to as a radio base station (RBS), can schedule downlink transmission to one user equipment (UE) on a plurality of downlink carriers simultaneously. MC-HSPA is sometimes alternatively referred to as multi-carrier HSPA. Multiple uplink carriers may also be activated. Carriers that can be dynamically activated/deactivated are referred to as secondary carriers. A secondary carrier may be secondary downlink carrier or a secondary uplink carrier. The uplink and downlink carriers that cannot be deactivated are referred to as primary or anchor carriers. In 3GPP specifications a secondary downlink carrier is also referred to as a secondary serving HS-DSCH (High-Speed Downlink Shared Channel) cell and a secondary uplink carrier is also referred to as a secondary uplink frequency.
Currently 3GPP is standardizing 4-carrier high speed downlink packet access (4-carrier HSDPA for short) within the scope of Rel-10 (Release 10). 4-carrier HSDPA is an evolution of Dual Cell HSDPA (DC-HSDPA) standardized in Rel-8, Dual-Band DC-HSDPA and DC-HSDPA with Multiple-Input Multiple-Output (MIMO), both standardized in Rel-9. With 4-carrier HSDPA the NodeB can schedule downlink transmission to one UE on up to four downlink carriers simultaneously.
One of the important features in MC-HSPA systems is the serving NodeB's ability to dynamically determine which of the downlink carriers that a certain UE needs to listen to and which uplink carriers that a UE should transmit physical control channels and potentially payload data on.
In the 3GPP standard Technical Specification (TS) 25.212, version 9.1.0, Mutiplexing and channel coding (FDD) dynamic NodeB initiated activation and deactivation of secondary carriers is accomplished by means of High-Speed Shared Control Channel (HS-SCCH) orders. An HS-SCCH order carries the following information:                order type information (3 bits), denoted xodt,1, xodt,2 and xodt,3,        order bits information (3 bits), denoted xord,1, xord,2 and xord,3,        UE identity, which is based on HS-DSCH Radio Network Identifier (H-RNTI) (16 bits).        
An order mapping defines the relationship between the desired outcome of the order and the order type and order bits that are transmitted to the UE. For example, the order type ‘000’ refers to DRX (Discontinuous Reception), DTX (Discontinuous Transmission), and HS-SCCH-less operation.
In MC-HSDPA systems dynamic deactivation of downlink carriers may be initiated due to several reasons. Examples include:                Improve the downlink performance of the primary downlink carrier by allowing the UE to reduce the bandwidth of its receiver filter.        Improve the UE battery life time by allowing the UE to turn off one receiver chain, e.g. in a case of Dual-Band HSDPA.        Reduce uplink overhead and/or improve uplink coverage by enabling the UE to utilize a different format for a High-Speed Dedicated Physical Control Channel (HS-DPCCH), the uplink channel used for HSDPA-related feedback from the UE to the serving NodeB.        
Similarly dynamic deactivation of uplink carriers in MC-HSUPA system could be initiated with the objective to:                Improve uplink coverage of, e.g. HS-DPCCH by not requiring the UE to transmit DPCCH on both uplink carriers.        Reduce hardware resource allocation in the Node-B, which is applicable to both serving and non-serving Node-Bs.        Improve radio resource utilization efficiency when multiple active UEs with data to transmit are present in the cell.        
An obvious reason for activating a secondary uplink or downlink carrier for a certain UE is to increase the instantaneous data rate.
In 4-carrier HSDPA there will be up to 4 downlink carriers that can be assigned to the same UE and up to 2 adjacent uplink carriers. The design of the HS-SCCH order mappings for 4-carrier HSDPA is currently being discussed in 3GPP and several order mappings have been proposed. Most of the proposed solutions address both 4-carrier HSDPA as described above and a scenario, potentially standardized in a future release, with up to 4 uplink carriers as well. In the proposed solutions both the NodeB and the UE would need to implement a lookup table in which a desired carrier activation status, i.e., a description of the secondary uplink and downlink carriers that should be active after successful HS-SCCH order reception, can be looked up. In a worst case scenario, the desired carrier activation status would however need to be compared with all possible carrier activation statuses listed in the lookup table before the corresponding HS-SCCH order can be determined.
Up to Rel-9 there are in total three HS-SCCH orders related to activation and deactivation of the secondary downlink and/or secondary uplink carrier. This small number of HS-SCCH orders facilitates solutions solely based on look-up tables. For 4-carrier HSDPA, with up to four downlink carriers and up to two uplink carriers configured, a total of twelve HS-SCCH orders related to carrier activation and deactivation, including the three specified in Rel-8 and Rel-9, will be possible. In a potential future release where UEs can be configured with four downlink and four uplink carriers the number of HS-SCCH orders related to the activation and deactivation will be as high as 27, including the three specified in Rel-8 and Rel-9. For such a large number of orders, solutions in which the NodeB and UE need to implement lookup tables and search through a large search space for determining which order that corresponds to a certain activation status of the secondary uplink and downlink carrier(s) may become inefficient. Hence it would be desirable to adopt an order mapping in which the Node-B and UE not necessarily need to rely on pure table lookup solutions.